in vec3 v_positionEC;
void main() {
  czm_materialInput materialInput;
                // 获取模型position信息
  vec4 position = czm_inverseModelView * vec4(v_positionEC, 1.0);
                //   根据高度来设置渐变颜色
  float strength = position.y / 100. + 0.4;
  out_FragColor = vec4(strength * 0.3, strength, strength, 1.0);
                //   动态光环
                //   czm_frameNumber获取当前帧数
                //   fract(x),返回x的小数部分
  float time = fract(czm_frameNumber / (60.0 * 10.0));
                //   float time  = fract(czm_frameNumber/60.0)*6.28 ;
                //   实现往返的操作
  time = abs(time - 0.5) * 2.0;
                // time = sin(time);
                // clamp(x, min, max)，返回x在min和max之间的最小值
  float diff = abs(clamp(position.y / 500.0, 0.0, 1.0) - time);
                // step(edge, x)，如果x大于等于edge，返回1，否则返回0
  diff = step(0.01, diff);
  out_FragColor.rgb += vec3(0.5) * (1.0 - diff);
}
